454 D&GRAS DEGRAS Genuine degras (natural degras) is a secondary product of the chamoising of skins. It consists of marine animal oil (especially whale oil), in which the action of atmospheric oxygen has led to the formation of resinous hydroxy-acids (Degragene), emulsified with water and containing small proportions of mineral substances (soda, lime, sulphates) and organic residues (hide, membranous fragments) resulting from the method of preparation. This product forms a fairly dense, almost pasty, yellow or orange liquid, which has a special odour recalling that of fish oil and remains homogeneous even on long standing. Artificial degras is obtained by mixing natural degras with fish, mineral or resin oil, vaseline, wool fat, tallow, etc., or by artificial oxidation of fish oils, followed by emulsification with water and sometimes by addition of the other extraneous substances mentioned above. Artificial degras is also a yellow or orange dense liquid, which is usually more liquid than the natural product and has a peculiar fish oil odour ; on long standing, it tends to divide into two layers, the water settling to the bottom. Analysis of degras includes various determinations and tests to serve as a guide in ascertaining if it is a natural or artificial product, if it is pure, that is, based solely on fish oils, or if it is mixed with tallow, wool fat, mineral oils, vaseline or resin oils, these being the most frequent additions to degras. The principal determinations are as follows : 1. Water.—10 grams of the degras are placed in a porcelain dish previously heated to redness with about 10 grams of coarse quartz sand and tared ; the fat is mixed well with the sand and the dish and contents dried at 120° until of constant weight (4-5 hours). The loss in weight gives the water. 2. Non-fatty Substances (Organic Residues).—20 grams of the degras are dried in an oven at 120° OF even over a direct flame, the liquid being stirred with a thermometer and care taken that its temperature does not exceed 105°; the dried product is dissolved in petroleum ether and the solution filtered through a tared filter, the insoluble mattei being washed with petroleum ether and then with a little ether or benzene and alcohol, dried at 100° and weighed. This insoluble matter consists principally of epidermis and hide residues readily recognisable with a lens or microscope, together with a few other impurities. On the other hand, evaporation of the petroleum solution and weighing of the residue dried at 105° gives the total fat; the latter is used for the determinations indicated under 4 (below), 3. Ash.—10 grams of the degras are carefully heated in a platinum dish over a naked flame until copious fumes are emitted, the dish being then heated more strongly on a sand-bath and finally in a muffle at a dull red heat. The ash is mainly alkali and alkaline-earthy sulphates ; it is fat.